Ecosystem Guidelines for Environmental Assessment

FRESHWATER
Water quality must be controlled to allow management of wetlands in relation to specific objectives,
e.g. some wetlands may be deemed suitable for improving water quality; others would need protection
from pollutants to maintain particular habitat quality.
Hydrological connections between systems should be preserved.
Existing ecosystem linkages/connectivity must be maintained at an appropriate scale.
Buffers (i.e. building setbacks, preferably natural vegetation) should:
- protect wetland systems from specific identified threats, as relevant to each system
- provide sufficient space to allow for future rehabilitation and buffering of that ecosystem
- protect the ecosystem health and integrity of receiving ecosystems.
What broad spatial guidelines can be given with respect to
the best approach to development and disturbance
Wetlands should be delineated prior to planning for development.
Wetland delineation and assessment should take place during the wet season; the level of confidence
attached to wetland identification and delineation in the dry season is very low for all wetlands other
than permanent systems.
Allow adequate buffering of rivers and drainage lines. Ideally, buffer areas should first make allowance
for future rehabilitation of the channel - e.g. regrading and reshaping of hardened river banks - and then
impose development setbacks from the theoretical edge of the rehabilitated river bank. The City of Cape
Town's Floodplain Management Guidelines 1 should be used as broad guidelines for minimum setback
areas. Additional evaluation of specific functional requirements of the buffer areas, on a site-specific
basis, is needed (e.g. providing an appropriate buffer width for a system receiving treated effluent
runoff, versus providing an adequate buffer against noise pollution or alien invasion).
Spatial depiction of existing or past linkages between wetlands, drainage channels and rivers/streams
(these should be maintained or restored wherever possible) is required.
Small wetland fragments should be linked by areas of open space; existing drainage lines and
corridors should be conserved; previously disturbed areas should be used, where ecologically appropriate,
for performing "services" such as stormwater treatment, leaving less disturbed areas in a relatively
unimpacted, more isolated condition.
Wetland services usually require a minimum size before they are effective. Note however that
multiple small systems may nevertheless have an important cumulative effect.
Appropriate unhardened terrestrial open space areas should be used as buffers/interfaces between
developments and wetlands, performing services such as initial filtration and sedimentation of runoff.
The land-use permitted in these areas should be in accordance with this function. The width of these
buffer areas should be determined with regard to their required functions. Land-uses that potentially
would add nutrients instead of performing a filtering function would be less appropriate, e.g. grazing
of livestock, development of feedlots or equestrian areas.
What are the critical things to maintain in terms of managing these
systems for biodiversity, and ensuring its persistence
Flow regime, including seasonality, water quantity and links to the water table and groundwater system.
Water quality.
Plant communities and habitat structure and zonation - invasion by opportunistic plant species can
occur rapidly and permanently alter habitat quality and availability. Active management against invasion
by opportunistic weeds and other invasive plant species such as bulrush Typha capensis and various
1. City of Cape Town (November 2000) Development Control Guidelines for Flood-prone Areas
- Draft edition. CCT Catchment, Stormwater and River Management, Catchment Management
Department, Cape Town.
FRESHWATER ECOSYSTEMS - WETLANDS : 71